Hi there! I have a 6 foot 125g reef tank and have it stocked with the following:
3 Blue reef Chromis
Male & Female Squareback Anthias'
Brown Barred Goby
Pink Spotted Watchman Goby
I find with the smaller tang, the tomini that is, that 3 Tangs is most likely the most you should go. The blue and the yellow are quite active and tend to race back and forth during the day.
I have smaller fish for the rest instead of larger ones so I have a nice mix. I can most likely add a fish or two, nothing huge of course and still be ok.
Alot depends on your maintenance routine and water changes as well as equipment. The more fish the higher bioload and the more effort you have to put in to keep the water fine. I've also been taking my time stocking, I have been adding fish for over a year now to get to this point.